code: def get_checkpoint_path(self) -> str | None:
      ckp_path = os.getenv("NNI_CHECKPOINT_DIRECTORY")
      if ckp_path is not None and os.path.isdir(ckp_path):
          return ckp_path
      return None
  
file_path: nni/nni/recoverable.py
imports: from __future__ import annotations
  import os
  import nni
label_desc: Use image node_id 4 for calling the Recoverable obj's underlying member method code with example usage: obj.get_checkpoint_path() and returns: None, ckp_path